fix: don't merge column header rows as continuations

Rows with 3+ short-valued cells (avg ≤10 chars) and an empty first cell
are column headers (e.g. "UR | SC | ST | OBC | EWS"), not text overflow
from the previous row. Prevents them from being merged into the
preceding section title row.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/tables/format.rs

@@ -112,10 +112,14 @@ fn clean_table_cells(cells: &[Vec<String>]) -> (Vec<Vec<String>>, Vec<String>) {
         // header like "Category No. 03 - ...") — these are spanning headers,
         // not overflow from the previous row.
         let has_long_spanning_cell = non_first_cells.len() == 1 && non_first_cells[0].len() > 15;
+        // Rows filling most columns with short values are header or data rows,
+        // not text overflow (e.g. "UR | SC | ST | OBC | EWS" column headers).
+        let looks_like_header_row = non_first_cells.len() >= 3 && avg_cell_len <= 10.0;
         let is_classic_continuation = first_cell.is_empty()
             && !non_first_cells.is_empty()
             && !is_short_subheader
             && !looks_like_data_row
+            && !looks_like_header_row
             && !has_long_spanning_cell
             && cleaned.len() > 1;
 

tests/snapshots/thermo-freon12.md

@@ -46,7 +46,9 @@ l
 
 |Temp|Pressure||Volume|||Density||Enthalpy|||Entropy|Temp|
 |---|---|---|---|---|---|---|---|---|---|---|---|---|
-|°C|[kPa]|[m3 Liquid v f|/kg]|Vapour v g|Liquid d f|[kg/m3] Vapour d g|Liquid H f|[kJ/kg] Latent H fg|Vapour H g|Liquid S f|[kJ/K-kg] Vapour S g|°C|
+|°C|[kPa]|[m3|/kg]|||[kg/m3]||[kJ/kg]|||[kJ/K-kg]|°C|
+|||Liquid||Vapour|Liquid|Vapour|Liquid|Latent|Vapour|Liquid|Vapour||
+|||v f||v g|d f|d g|H f|H fg|H g|S f|S g||
 
 |-100|1.2|0.0006|10.0000|1679.0|0.100|113.3|192.8|306.1|0.6077|1.7210|-100|
 |---|---|---|---|---|---|---|---|---|---|---|---|